This invention relates to a method and apparatus for controlling feed speed in a numerical control system which numerically controls the movement of a machine.
Numerical control systems are widely employed for numerically controlling the actions and movements of various machines, particularly machine tools. A numerical control system performs such control by supplying the servo system of the machine with feed pulses based on a commanded feed speed. Such a numerical control system has a feed speed override function for increasing or decreasing the commanded feed speed in accordance with a separately entered ratio, referred to as an override quantity. The feed speed override function makes it possible to change a commanded feed speed, which has already been programmed into the system, or a jog feed speed given by a parameter, into an optimum feed speed when desired.
According to the prior art, the feed speed override function is realized by providing an operator's panel, located on the machine side, with override quantity setting means that are utilized to change the override quantity in analog or digital fashion. This is a disadvantage, however, since such an arrangement requires the provision of special switches to serve as the override setting means, as well as numerous signal lines to carry the associated signals. The number of such lines becomes particularly large when the arrangement is such as to enable fine setting of the override quantity.